This invention relates to accelerated strength testing of concrete.
With present practice, the quality of Portland cement concrete is based on the 28-day compressive strength of a specimen. However, in many concrete construction projects, a rapid and reliable prediction of the standard 28-day compressive strength would be advantageous. Early strength prediction can save expense by avoiding situations where the concrete does not reach the required design strength or by avoiding concrete that is unnecessarily strong. An accurate accelerated test of a concrete mix would allow rapid changes in the mix to be made to conform with specifications.
A number of methods for providing accelerated strength testing of a concrete mix have been proposed. The methods proposed include applying heat to specimen by means of saturated steam, hot water, autoclaving, dry oven heat, electrical heat or autogenously. None of these previously proposed methods have been found to be entirely satisfactory. In known methods which utilize heat to accelerate curing, a precuring step is commonly used to partially cure the specimen in order to prevent specimen separation in the subsequent heating step. However, this precuring step adds significantly to the time required. In proposed methods that attempt to provide early strength prediction, the ratio of the compressive strength to the standard 28-day strength is relatively low, and such methods, therefore, have low reliability, particularly when there are variations in the composition of the concrete mix.